Bacterial vaginosis is not classified as a sexually transmitted infection. By definition, an STI is caused by a pathogen that comes from outside the body, while BV results from an overgrowth of bacteria that already live in the vagina. That said, the relationship between BV and sex is real and significant, which is exactly why this question comes up so often.
Why BV Isn’t Considered an STI
A healthy vagina contains large numbers of Lactobacillus bacteria, which produce lactic acid and hydrogen peroxide to keep the environment slightly acidic and inhospitable to harmful microbes. BV develops when those protective bacteria get displaced by an overgrowth of other organisms that are normally present in small numbers. The key distinction is that none of these bacteria are foreign invaders passed from one person to another the way chlamydia or gonorrhea would be. The problem is an internal shift in balance, not an imported infection.
The CDC describes BV as a “vaginal dysbiosis,” essentially an ecosystem thrown out of whack. Researchers still don’t fully understand what triggers that shift, and whether a single sexually transmitted pathogen plays a role remains an open question. But as things stand, BV does not meet the technical definition of an STI.
The Strong Link to Sexual Activity
Even though BV isn’t an STI, it rarely occurs in people who have never had sex. New sexual partners, multiple partners, and unprotected sex all increase the risk. Sex can introduce new bacteria or change the vaginal environment in ways that tip the microbial balance. Researchers don’t yet know the exact mechanism, but the pattern is consistent enough that safe sex practices, including condom use, are recommended to reduce BV risk.
This gray area is what confuses most people. BV behaves in some ways like an STI (it’s associated with sexual activity, it’s more common with new partners) but in other ways it doesn’t (it can occur without sex, it’s caused by bacteria already present in the vagina, and treating a male partner has not been shown to prevent recurrence in standard guidelines). Think of it less like catching something and more like a disruption that sex can trigger.
Common Symptoms
Many people with BV have no symptoms at all. When symptoms do appear, the most recognizable is a thin, grayish-white vaginal discharge with a distinct fishy odor, often stronger after sex. The vaginal pH rises above 4.5, which is higher than normal. Unlike a yeast infection, BV typically doesn’t cause significant itching or thick, clumpy discharge, so the two are often confused but feel quite different.
How BV Is Diagnosed
Diagnosis usually happens during a pelvic exam. Clinicians look for at least three of four signs: the characteristic thin discharge, elevated vaginal pH, a fishy smell when a chemical solution is applied to a sample, and the presence of “clue cells” (vaginal cells coated with bacteria) under a microscope. A lab-based scoring method that examines the ratio of Lactobacillus to other bacterial types under a microscope can also confirm the diagnosis, with scores of 7 or higher (on a 0 to 10 scale) indicating BV.
Treatment and the Recurrence Problem
BV is treated with prescription antibiotics, typically taken orally or applied as a vaginal gel or cream. Most people respond well to the initial course of treatment, but recurrence is extremely common. In one study published in The Journal of Infectious Diseases, 23% of women had a recurrence within one month of completing oral antibiotic therapy. By three months, that figure climbed to 43%. By 12 months, 58% had experienced at least one recurrence.
These high recurrence rates are part of the reason BV is so frustrating to manage. The antibiotics clear the overgrown bacteria, but they don’t necessarily restore the Lactobacillus population to its previous strength, leaving the door open for the same imbalance to return.
What Raises Your Risk
Beyond sexual activity, several habits and exposures can disrupt the vaginal microbiome and increase BV risk:
- Douching is one of the most well-documented risk factors. It strips away Lactobacillus, raises vaginal pH, and weakens the vagina’s natural defenses. The vagina is self-cleaning, and douching directly undermines that process.
- Scented soaps, shower gels, and feminine hygiene products used internally or around the vaginal opening can irritate tissue and disrupt bacterial balance. These products are not formulated for vaginal use.
- New or multiple sexual partners increase exposure to different bacterial profiles, which can destabilize the existing microbial community.
- Not using condoms is consistently associated with higher BV rates, likely because semen is alkaline and temporarily raises vaginal pH.
Why Untreated BV Matters
BV often resolves on its own, and many people live with it without knowing. But leaving it untreated carries real risks, particularly during pregnancy. A meta-analysis of 20 studies covering more than 290,000 women found that BV nearly doubles the risk of preterm birth. That association is strong enough that some researchers have called for routine BV screening during prenatal care.
Outside of pregnancy, BV makes you more susceptible to actual STIs. The loss of protective Lactobacillus and the rise in vaginal pH create an environment where pathogens like HIV, chlamydia, and gonorrhea can take hold more easily. BV also increases the risk of infection after gynecological procedures.
Protecting Your Vaginal Microbiome
The most effective prevention strategies center on not disrupting the bacterial balance that keeps BV away. Skip douching entirely. Wash the external genital area with warm water only, or at most a mild, unscented cleanser, and avoid getting any product inside the vaginal canal. Use condoms with new partners. These steps won’t guarantee you’ll never get BV, but they meaningfully reduce the odds.
If you’ve had BV before, pay attention to patterns. Some people notice recurrences after specific triggers, whether that’s a new partner, a particular product, or a course of antibiotics for something else. Identifying your personal triggers can help you and your healthcare provider build a longer-term management plan, especially given how common recurrence is.